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　　Thermal stress and microstructure stress exist in seamless steel pipe of seamless steel pipe factory during heat treatment. This internal stress can be superimposed or partly offset each other. It is complex and changeable because it can change with the change of heating temperature, heating speed, cooling mode, cooling speed, part shape and size, so heat treatment deformation is inevitable. Of course, the mechanical collision of seamless steel pipe in the heat treatment process will cause the deformation of parts, but this deformation can be reduced and avoided by improving the operation.

　　In the heat treatment process of API 5L ASTM A106 seamless steel pipe in seamless steel pipe factory, if the seamless steel pipe is heated in oxidizing medium, the surface oxidation will occur, which will reduce the mass fraction of carbon on the surface of the parts and cause the surface decarbonization. The depth of the decarburization layer exceeds the final processing allowance and the parts will be scrapped. The surface decarburization depth can be measured by metallographic method and microhardness method. The method of measuring the microhardness distribution curve of the surface layer is the criterion and can be used as an arbitration criterion.

　　Due to insufficient heating, poor cooling, improper quenching operation and other reasons, the local surface hardness of seamless steel pipe in seamless steel pipe factory is not enough, which is called quenching soft spot. Like surface decarbonization, it can cause a serious drop in surface wear resistance and fatigue strength.

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